7. Reactions following immunization

Although modern vaccines are extremely safe, some vaccines may
lead to reactions. The occurrence of an adverse event after the administration
of a vaccine, however, does not prove that the vaccine caused the symptoms. An
association between an adverse event and a specific vaccine is suggested:

· if there is an
unusual clustering of a condition in vaccinees in a limited interval after
immunization, or

· if vaccinees experience the
event at a rate significantly higher than that in groups of similar age or
background who have not recently received a vaccine.

Adverse reactions may be caused by faults of administration
(programmatic errors) or be associated with the properties of vaccines.

7.1 Programmatic errors

The most common adverse events caused by programmatic errors are
abscesses following inadvertent inoculation into the superficial layer of the
skin of poorly mixed adsorbed vaccines (sterile abscesses), and abscesses that
arise because needles and syringes are not sterilized properly. Serious adverse
events may arise if vaccines are given to persons for whom they are truly
contraindicated, for example BCG and measles vaccines can cause disseminated
disease in immunosuppressed individuals.

7.2 Reactions related to inherent properties of vaccines

Adverse events may be caused by reactions to the immunizing
antigen itself or to other components of the vaccine, such as antibiotics
(kanamycin or neomycin in measles vaccine, streptomycin or neomycin in OPV), a
preservative (merthiolate, a mercury-containing compound present in DPT, DT and
TT) or aluminium adjuvant present in adsorbed vaccines.

Adverse events range from mild (for example, a transient fever
or local irritation following DPT vaccine) to serious (e.g. vaccine-related
paralysis following OPV immunization). Mild local reactions following DPT
vaccine are quite frequent and occur in 20% - 50% of vaccinees. Rarely occurring
sterile abscesses have been reported following immunization with vaccines
containing an increased amount of aluminium adjuvants (Bernier 1981).
Fever and rash after administration of measles vaccine and tenderness, redness
and swelling after typhoid or cholera immunization are other examples of mild
adverse reactions following immunization.

Localized and regional adenitis and prolonged ulceration
resulting from BCG immunization may be related to the strain of BCG bacilli in
the vaccine and often occur after a change in the source of vaccine used in a
country. Some substrains of BCG appear to be more likely to cause adenitis than
other substrains. Axillary or cervical lymphadenitis usually heals spontaneously
and it is best not to treat the lesion if it remains unadherent to the skin. An
adherent or fistulated lymph gland, however, may be drained and an anti-TB drug
may be instilled locally. Some authors recommend systemic treatment of severe
persistent lesions with erythromycin (Bhandari et al. 1980), while others
have tried systemic treatment with isoniazid (Hanley et al. 1985).
However, lesions have persisted despite one month of therapy with either drug,
and placebo-controlled trials of treatment are needed (Hanley et al.
1985). BCG infection that may occur in immunosuppressed individuals should be
treated with anti-tuberculous drugs (Romanus et al. 1993).

Some persons, especially in older age groups, may have a
hyperimmune reaction to diphtheria toxoid, or more rarely tetanus toxoid, after
receiving booster doses of those vaccines when they have high litres of the
respective antitoxin. Some live virus vaccines prepared on hens egg
tissues, such as yellow fever or influenza vaccines, may have a potential risk
for egg-sensitive individuals. However, only a few reactions are clearly
associated with specific hypersensitivity.

Severe reactions are extremely rare. Major reactions include
encephalitis after mumps and measles vaccines, encephalopathy after pertussis
vaccines, and paralysis after oral polio vaccine among recipients of the vaccine
or their contacts. The risk of OPV-related paralysis has been estimated through
passive surveillance in the USA, where about one case has occurred per 2.5
million doses of OPV distributed during 1980-1989 (Strebel et al. 1992).
Many adverse events have been reported as related in time to DPT immunization.
However, a comprehensive analysis of the relationship between various events and
immunization against pertussis did not indicate a causal relationship between
DPT immunization and infantile spasms, Reyes syndrome, or sudden infant
death syndrome. There is insufficient evidence to indicate the presence (or
absence) of a causal relation between pertussis immunization and aseptic
meningitis, chronic neurological damage, Guillain-Barre syndrome, haemolytic
anemia and other conditions (Howson and Fineberg 1992a). On very rare
occasions, DPT immunization may cause acute encephalopathy, convulsions, or
shock-like state or hypotonic and hyporesponsive episodes (Cody et al.
1981, Howson and Fineberg 1992b).

Although the rates of serious events are difficult to estimate
precisely, they are far less frequent than the complications caused by the
disease themselves (Table 11).

The detection of serious adverse events following immunization
is important for the success of a programme, since such events can influence
community acceptance of immunization. In developing countries, the majority of
complications recognized following immunization appear to be programme related;
thus the underlying causes of these cases need to be identified and corrected.

The policy recommended by EPI is:

· All immunization programmes
should monitor adverse events following immunization. A field guide for
surveillance of adverse events has been produced (EPI 1993f). Each adverse event
should be investigated and efforts should be made to determine its cause. The
detection of adverse events should be followed by appropriate treatment and
communication with parents, health workers, and if several persons are affected,
with the community. If the adverse event was determined to be due to programme
errors, operational problems must be solved, by appropriate logistical support,
training and supervision.